The size of the opening is controlled by the nervous system: at rest, the parasympathetic nervous system constricts the pupil and in danger, the sympathetic nervous system supplies the pupillary dilator muscle to enlarge the pupil.

The halecostomes, of which Amia is an example, have an opercular dilator muscle originating on the mandible which opens the operculum.

The anesthesia care provider takes special care to ensure the removal of all esophageal tubes during insertion of sizing tubes, such as bougie dilators.

The dilator is removed and the nasogastric tube placed through the gastrojejunostomy and into the Roux limb.

Interestingly, in one of these reports all stenoses were at the level of the tracheostomy, and the authors suggested that tracheal damage from the inward force of the graded dilators might be the cause.